An important consideration when regarding syringes is to ensure that the plunger can move at a constant speed and with a constant force when it is pressed into the barrel. For this purpose, a lubricity layer, either on one or on both of the barrel and the plunger, is desirable. A similar consideration applies to vessels which have to be closed by a stopper, and to the stopper itself, and more generally to any surface which should provide a certain lubricity.
In glass syringes, silicon oil is typically used as a lubricant to allow the plunger to slide in the barrel. Silicon oil has been implicated in the precipitation of protein solutions such as insulin and some other biologics. Additionally, the silicon oil coating is often non-uniform, resulting in syringe failures in the market.